Method of processing metal powder

ABSTRACT

The invention relates to a method of processing metal powder consisting a plurality of metal powder pellets, comprising the following steps:
         heating the metal powder pellets until they are in a liquid state,   causing a collision of the liquefied metal power pellets with a heated impact body, the temperature of which is higher than the melting point of the metal powder pellets, to form metal powder pellets of reduced diameter,   cooling the metal powder pellets of reduced diameter formed in the collision and   collecting the cooled metal powder pellets of reduced diameter in a collecting vessel.

The invention relates to a method of processing metal powder consisting of a plurality of metal powder pellets.

A method of producing steel powder consisting of plurality of steel powder pellets is already known. In this known method a steel melt is produced. This is transferred to a container and acted on there by N₂ gas so as to effect an atomisation of molten steel with use of nitrogen gas. By means of this known method, which is performed in a protective gas atmosphere, steel powder is produced which consists of a plurality of steel powder pellets having a diameter in the range between 100 microns and 500 microns.

It has proved that it is advantageous or even necessary for certain industrial applications to make available metal powder with metal powder pellets of reduced diameter.

The object of the invention consists in indicating a method of processing metal powder consisting of a plurality of metal powder pellets, by means of which it is possible to produce metal powder with metal powder pellets reduced in size.

This object is fulfilled by a method with the features indicated in claim 1. Advantageous embodiments and developments of the invention are evident from the following explanation thereof with reference to the figures, in which:

FIG. 1 shows a flow chart for explanation of a method of processing metal powder according to a first exemplifying embodiment for the invention,

FIG. 2 shows a flow chart for explanation of a method of processing metal powder according to a second exemplifying embodiment for the invention and

FIG. 3 shows a flow chart for explanation of a method of processing metal powder according to a third exemplifying embodiment for the invention.

Provided as starting material for the method according to the invention is metal powder consisting of a plurality of metal powder pellets having a diameter in the range of 100 μm to 500 μm. Metal powder of that kind can be produced, for example, by means of the above-mentioned method.

In accordance with the method according to the invention there is carried out—as is evident from FIG. 1—in a first step S1 a heating of the metal powder pellets to a temperature at which the metal powder pellets are in a liquid state. This heating of the metal powder pellets can be undertaken with use of an induction process, through a use of radiant heat or in a hot protective gas flow.

In a second step S2 following thereupon a collision of the metal powder pellets in liquid state with a heated impact body is produced, the temperature of the impact body being higher than the melting point of the metal powder pellets. Through this collision the metal powder pellets break into pieces and the metal powder pellets of reduced diameter are formed. It is ensured by the heating of the impact body that the metal powder pellets impinging on the impact body are not welded to the impact body.

The impact body can be an impact plate extending at a right angle or another angle to the metal powder pellet flow. This impact plate can be of propeller-shaped construction. Moreover, it can be constructed to be movable, for example rotating or constantly pivoted.

The metal powder pellets of reduced diameter formed by collision with the impact plate are, in accordance with a succeeding step S3, cooled. This cooling already begins directly after formation of the metal powder pellets of reduced diameter on the way to a collecting vessel in which they are collected in a step S4. According to step S5, cooling of the metal powder pellets takes place in the collecting vessel until these are in a solid state.

An alternative embodiment consists in that the metal powder pellets in liquid state collide with one another in order to obtain metal powder pellets of reduced diameter.

The metal powder pellets obtained by the method described in the foregoing have, by contrast to the starting material, a reduced diameter. They can accordingly be used for applications which require metal powder of which the metal powder pellets have a smaller diameter than the metal powder pellets of the metal powder present as starting material.

This is the case, for example, when metal powder, which consists of a plurality of metal powder pellets of reduced diameter of that kind, is used for production of a drilling tool of, for example, steel with internally disposed helically extending cooling channels, wherein the steel powder is kneaded together with a binder, the steel powder kneaded together with the binder is led through a press-moulding tool in order to produce a strand with internally disposed rectilinear cooling channels, the strand leaving the press-moulding tool is respectively cut to a desired length, the blank arising in that case is, with support over its entire length, subjected to a rolling movement at a speed which linearly and constantly changes over the length of the body so that the blank is twisted, and the twisted blank is sintered and then provided at its outer circumference with helically extending cutting grooves. Very high demands with respect to maintenance of predetermined dimensions exist with blanks of that kind.

Tests have shown that production of drilling tools of that kind of steel with internally disposed helically extending cooling channels is not possible with use of steel powder, such as is used as starting material for the method according to the invention, and with use of the method described in the preceding paragraph, since the blank produced is unstable in shape. If, thereagainst, the steel powder which is produced by means of the method according to the invention and which comprises steel powder pellets of reduced diameter is used for producing drilling tools of steel with internally disposed helically extending cooling channels by means of the method described in the preceding paragraph, then the desired end products can be produced, since the formed blank is stable in shape and can be further processed in desired manner by means of the sintering process. This is attributable to the fact that in the twisted blank the steel powder pellets are more densely packed so that the desired shape of the blank is maintained.

An improved method for processing metal powder is explained in the following with reference to the flow chart shown in FIG. 2.

In this improved method as well, in which the same metal powder is used as starting material as in the case of the method explained with reference to FIG. 1, heating of the metal powder pellets is carried out in a first step S1 to a temperature at which the metal powder pellets are in a liquid state.

In a succeeding step S1/2 the metal powder pellets in liquid state are subjected to an acceleration. This acceleration can be undertaken by a magnetic field, by means of a centrifuging process or by means of a protective gas flow.

The accelerated metal powder pellets in liquid state are subjected in a succeeding step S2 to a collision with a heated impact body in order, just as in the case of the method explained with reference to FIG. 1, to break up into metal powder pellets of reduced diameter.

The metal powder pellets of reduced diameter formed by the collision are cooled in accordance with a succeeding step S3. This cooling already begins directly after formation of the metal powder pellets of reduced diameter on the way to a collecting vessel in which they are collected in accordance with a step S4. The metal powder pellets of reduced diameter there finally cool in a step S5 until they are present in a solid state. Alternatively thereto, the metal powder pellets of reduced diameter produced by step S3 can be subjected in the collecting vessel, in which they are collected in accordance with the step S4, to another processing.

Through the described acceleration of the metal powder pellets in liquid state the kinetic energy thereof is increased so that the metal powder pellets on impact thereof with the impact body break into pieces even better than in the case of the exemplifying embodiment described with reference to FIG. 1. This has the consequence that the number of metal powder pellets of reduced diameter formed when breaking into pieces is increased and the diameter of the metal powder pellets formed when breaking into pieces is further reduced. The stability of shape of the blanks formed in the above method is thereby further improved.

In accordance with the present invention, metal powder consisting of a plurality of metal powder pellets is moreover processed in such a manner that metal powder is provided which consists of a plurality of metal powder pellets of reduced diameter.

According to an advantageous development of the method described with reference to FIGS. 1 end 2 a screening of the metal powder pellets of reduced diameter formed by the collision is carried out between the steps S3 and S4 in a step S3/4. The object of this screening is to return to the process metal powder pellets having a diameter which as before is greater than a desired maximum diameter, so that these metal powder pellets can be reheated and subjected to a collision again in order to provide metal powder pellets of reduced diameter, wherein these reduced diameters are smaller than or at most equal to the desired maximum diameter.

An example of a method in which a screening of that kind is carried out is illustrated in FIG. 3. According to this method illustrated in FIG. 3 the metal powder pellets of reduced diameter, which were already cooled in step S3 are subjected in a step S3/4 to a screening process. Those metal powder pellets having a diameter smaller than or equal to the desired maximum diameter pass through the screen and are collected in step S4 in a collecting container in which they are cooled in step S5 until they are in a solid state. Those metal powder pellets having a diameter greater than the desired maximum diameter are screened out and fed back to the step S1 so as to be reheated, thereafter accelerated in step S1/2 and then subjected in step S2 to a collision with the heated impact body.

Alternatively thereto, a screening can also be undertaken in the collecting container. This is indicated in FIG. 3 by dashed lines. 

1. Method of processing metal powder consisting a plurality of metal powder pellets, comprising the following steps: S1: heating the metal powder pellets until they are in a liquid state, S2: causing a collision of the liquefied metal power pellets with a heated impact body, the temperature of which is higher than the melting point of the metal powder pellets, to form metal powder pellets of reduced diameter, S3: cooling the metal powder pellets of reduced diameter formed in the collision and S4: collecting the cooled metal powder pellets of reduced diameter in a collecting vessel.
 2. Method according to claim 1, further comprising the following step: S5: cooling the collected metal powder pellets of reduced diameter until they are in a solid state.
 3. Method according to claim 1, wherein an acceleration of the heated metal powder pellets takes place between the heating of the metal powder pellets and the causing of a collision.
 4. Method according to claim 1, wherein the heating of the metal powder pellets is carried out with use of an induction process, by radiant heat or in a hot protective gas flow.
 5. Method according to claim 3, wherein the acceleration of the metal powder pellets is carried out by a magnetic field, by means of a centrifuging process or by means of a protective gas flow.
 6. Method according to claim 1, wherein the impact body is an impact plate.
 7. Method according to claim 6, wherein the impact plate is of propeller-shaped construction.
 8. Method according to claim 6, wherein the impact plate is constructed to be movable.
 9. Method according to claim 1, wherein the metal powder pellets of reduced diameter are subjected to a screening process and those metal powder pellets which do not run through the screen are reheated and subjected to a collision and those metal powder pellets which pass through the screen are collected in the collecting vessel.
 10. Method according to claim 1, wherein the causing of the collision is carried out in a vacuum or in a protective gas atmosphere.
 11. Method according to claim 1, wherein the heated metal powder pellets are brought against one another for the collision. 